Square wave generator



Sept. 22; 1953 J. w. GRAY 2,653,242

SQUARE WAVE GENERATOR,

Filed June 23, 1950 m pur I I l E E d 7 Q 3nventor JOHN MGR/1y attorney not been reliable enough Patented Sept. 22, 1953 2,653,242 SQUARE WAVE GENERATOR.

John W. Gray, White Plains, N. Y., assignor to General Precision Laboratory Incorporated, a

corporation of New York Application June 23, 1950, Serial No. 169,971

1 11 Claims.

This invention pertains to a square wave generator and more particularly to a free-running multivibrator so constructed and arranged as to start automatically without necessitating the application of an externally generated trigger pulse to insure operation thereof.

Multivibrators of the type termed free-running or a stable produce an alternating output potential spontaneously, without necessitating the impression of periodic pulses or triggers on the input thereof to initiate each cycle or half cycle of the potential produced at the output there- Such multivibrators may be constructed to generate a symmetrical output the frequency of which is directly proportional to a direct current signal potential applied to the input.

A common deficiency in such circuits, however, is that they may not'start to generate oscillations when first turned on. This misoperation occurs because in the absence of any transient pulse tending to reduce either one of the control electrodes, of two tubes interconnected as a multivibrator, below its out off potential, both control electrodes are initially conducting current, due to the positive potential of the direct current input signal, and both tubes jwill be conductive. Under these conditions the anode current in each tube is limited only by the limiting anode resistor. As a result, each anode assumes a potential but a few volts above its cathode potential and the gains 01 both tubes may be below unity. Self-oscillation of the multivibrator is then impossible. In order to initiate self-oscillation it is necessary to disturb the bottomed state of at least one of the tubes, as by introducing a strong transient pulse somewhere in the circuit, and this introduction lias in the past been accomplished by some manual expedient, such as by opening and closinga switch in the connection of one of the anodes. This lack of automatic starting has been a serious limitation on the utility of all free-running multivibrators, so much so that this very valuable and unique type of square wave generator has been limited in its application to laboratory-type apparatus, since it obviously has for use in unattended field equipment.

The instant invention overcomes these disadvantages heretofore inherent in such devices by providing an arrangement whereby pulses are automatically supplied to start the multivibrator when it is turned on. Thus no manual attendance is necessary and the device may be incorporated in unattended equipment with assurance that proper operation will be attained at all times.

Additionally the instant invention utilizes an arrangement for supplying pulses to initiate automatic and proper operation in a circuit such that at the instant of operation of the multivibrator the operation of the automatic starting means is discontinued so that the starting means has no effect on the operation of the multivibrator other thanas a means to initiate the operation thereof. Thus precision of and accuracy of operation is insured at all times.

The present invention also contemplates an arrangement such that the peak-to-peak poten-' tial of the square wave output thereofis maintained constant regardless of changes in the potential of the filament supply so that not only is an output assured but in addition its constancy is greater than heretofore attained.

These purposes and results are attained in general by the use of a relaxation oscillator and a pair of discharge tubes so connected in circuit with the multivibrator tubes and the potential supply therefor, that as long as both multivibrator tubes conduct in contradistinction to their proper mode of operation of one tube being nonconductive while the other is conductive, pulses are supplied by the relaxation oscillator to one of the tubes tending to render it non-conductive and so initiate proper operation. At the same time the relaxation oscillator and its associated tubes are so connected in circuit that the nonconductivity of either one of the multivibrator tubes inhibits further operation of the relaxation oscillator so that when the multivibrator is operative the relaxation oscillator has no effect thereon.

Additionally the pair of tubes connected in circiut with the relaxation oscillator and the multivibrator are so connected in relation to the supply source and the multivibrator tubes that variation in supply which tends to alter the peak-topeak output by reason of change in potential on the electrodes of the multivibrator tubes produces such a change in potential on the electrodes of the pair of tubes connected in circuit therewith as to introduce compensatory change in the output potential.

The invention will be more readily understood from the following detailed description when con-- sidered together with the accompanying drawings in which:

Figure 1 is a schematic diagram of a preferred form of the invention.

Figure 2 is a group of curves illustrating the operation of the circuit of Fig. 1.

Referring now to Fig. 1 discharge tubes ll and I2 are interconnected to constitute a mul- 3 tivibrator, the anode [3 of tube ll being connected through a small condenser H to the control grid l6 of the tube l2, while the anode I! of the tube 12 is similarly connected to the control grid 19 of the tube ll through a similar small condenser I8. Positive potential is supplied to the anode l3 from the +3 supply source through an anode resistor 2i and to the anode I! through resistor 22, the multivibrator output potential being derived from the anode terminal 31. The cathodes 24 and 26 of the tubes H and I2 are directly connected to ground and the screen electrodes 21 and 23 are energized from the positive +B source through the resistor 29. The control electrodes l6 and I9 are respectively connected through resistors 32 and 33 to a suitable source of direct current input potential connected between terminals 34 and 36. These grid bias resistors are equal, resulting in a multivibrator output potential wave form having symmetrical positive and negative loops. If these resistors be made unequal, the output loops will be unequal in duration, which is useful in some cases. The direct current input may be made variable or adjustable to thereby vary the frequency of the multivibrator output signal. One terminal 35 may be grounded.

Preferably, although not necessarily, the tubes I l and 12 are of the beam-power type as, for example, that designated as 6V6, since such tubes produce more precise results.

The operation of the multivibrator as so far described, and disregarding other portions 01' the circuit for the present, is as follows. Let it be assumed that current has been flowing for the greater part of a half cycle in the tube II, and that meanwhile no current has been flowing in tube l2. The potential of the anode I3 is therefore low because of the potential drop produced by the anode current in resistor 2| while the potential of the anode I1 is relatively high. These potentials are depicted in the curves P and P of Fig. 2, P being the potential of the anode l3, relatively low at the start, and P being the higher potential of the anode [1. The potential of control grid l9 oi' the conducting tube H is maintained in quiescent condition at a potential'very nearly that of the grounded cathode 24, the exact level de ending on the current flowing into the grid through resistor 32. This is indicated in Fig. 2 by the solid line G. The grid IS, on the other hand, is rising in potential, as shown at the beginning of the curve G, because at the time when the tube i2 was made non-conductive at the beginning of the half cycle under consideration the non-conductivity of tube l2 was produced by a. negative pulse of potential occasioned by and equal in amount to the abrupt fall in potential of the anode l3 and transmitted throu h condenser l4 to the grid It. Return of the potential of the grid side of the condenser l4 toward the potential of the input terminal 34 is then possible only by current flow through resistor 33 so that recovery occurs at a rate dependent on the product of the values of the condenser 14 and resistor 33. This rate is approximately exponential and is indicated by the dotted extension of the G curve, which is asymptotic to the control potential E of the terminal 34. However, this curve is shown dotted beyond the time t1 to indicate that the potential rise is not permitted to progress beyond that time, for by then the potential G has risen sufiiciently for current to begin to flow in the tube I2. This current flow produces a potendenser I4.

tial drop in the resistor 22, resulting in a drop in potential of anode II, which is communicated through the condenser 18 to the grid I9, tending to cut off tube l I.

The effect is cumulative and the anode current in tube l2 rapidly reaches a maximum while the potential G of the grid l9 falls precipitously and the anode current in tube l I is cut oif. Thus the potentials of the two anodes l3 and I1 and two grids I6 and I9 are reversed as is seen immediately following the time iii, in Fig. 2. The potential G 01' the grid l8 rises at time t1 slightly above zero potential because of the strong positive pulse originated by the rise oi the anode l3, communicated through the con- The drop in potential P of the anode I1 is nearly instantaneous, while the rise in potential P of the anode 13 although very rapid is approximately exponential approaching +B as an asymptote.

The multivibrator half-period is the time of rise of the nearly straight curve ab in Fig. 2, depending on the time constant of the condenser l4 in series with the resistor 33, or of the equal condenser-resistor combination composed of the condenser I8 and resistor 32, and also depending on the magnitude of the drop in anode potential of the other multivibrator tube, so that the half period t1, its is to a close approximation directly proportional to the potential of the terminal 34. If this potential is increased the slope of the line ab is increased thus reducing the halfperiod between t1 and tz, while if the potential E be decreased, the slope is decreased and the half-period is increased, the linearity and stability of this frequency control being excellent.

As so far described, the upper potentials of P and P' would be that of the supply source, namely, +B. In order to limit the anode rises to the steepest parts of their exponential curves and therefore to make them more abrupt, pro-- ducing a more nearly rectangular output, two triodes 38 and 39 are provided to act as plate catchers. In thus serving, each triode grid and associated cathode functions as a limiting diode to limit the potential rise of the multivibrator output beyond a predetermined point. To accomplish this function the control grid 4| of the triode 38 is connected to the multivibrator anode l3, while the control grid 42 oftriode 39 is connected to the multivibrator anode H. The triode cathodes 43 and 44 are placed at a positive potential less than that of the supply source +B by connecting them to the Junetion 10 of a potential divider composed of the resistors 46 and 41 in series between the +B potential source and ground. The triode anodes 53 and 54 are connected to the +B positive potential source through a common resistor 52.

Inasmuch as the grid 4| of the triode 38 is connected to the anode 13 of the multivibrator tube I I, while the grid 42 of the triode 39 is connected to the anode I! of the multivibrator tube l2, no current will flow in the triode 38 when the potential of the anode I3 is considerably less than that of the potential of the junction p to which the cathode 43 of the triode 38 i connected and likewise no current will flow in the triode 39 when the potential of the anode I1 is less than that of the potential of the junction p to which the cathode 44 is also connected. However, when the potential of the anode 13 tends to rise above the potential of the junction 12 current will flow through the circuit consisting of the resistor 2|, grid 4|, cathode 43 and junction p producing an increased potential drop in the anode resistor 2| which increase in potential drop is just sufllcient to maintain the potential of theanode :I 3 at that'of the junction p. Similarly the potential of the anode I1 is permitted to rise only to the potential of the junction 11 by the limiting action of the circuit comprising resistor 22, grid 42 and cathode 44. Thus as illustrated in Fig. 2 the curves P and P rise to a potential Ep representative of the potential of the junction p and are fiat. topped at this level.

The alternating peak-to-peak potential of the multivibrator wave form is thus made definite and constant. The upper peak is determined by the potential of the junction 1) through the described limiting diode action of the two triodes 38 and 39, while the lower peak potential is fixed at a specific amount above ground by the amount of beam power tube drop during the maximum current flow that is permitted by the beam power anode resistor.

Use of the limiting tubes also eliminatesmost output potential variation and consequent frequency variation that would otherwise be occasioned by variations in multivibrator filament potential and temperature; for any increase of filament voltage that lowers the effective potentialof the multivibrator cathodes 24 and 26 and therefore of the anodes l3 and I! also lowers the effective potentials of the triode cathodes 43 and 44 and therefore of the grids 4i and 42, when the triodes and beam powertubes all are operated from the same filament supply source. These changes substantially cancel'each other, because any increase of multivibrator filament temperature lowers the lower peaks of the output potential wave but a concomitant increase of triode filament temperature lowers the upper peak by the same amount, so that the peak-topeak potential remains constant. I

As before stated, it is not only possible but al together likely that the multivibrator of Fig. l-

as so far described will, when first turned on, be in such condition that full current fiows through both tubes Ii and I2, both anodes l3 and H are at the potential d, Fig. 2, and such condition will continue until a potential surge, fortuitously or deliberately introduced, disturbs at least one of the tube element potentials enough to initiate a regenerative interaction between the tubes to start generation.

In the instant invention potential surges or pulses are automatically generated and applied to the multivibrator until is commences to generate, at which time the initiating surges are, discontinued. This is accomplished by the provision of a neon tube 48 connected to operate as a relaxation oscillator. One electrode 49 of the neon tube 48 is connected to'the constant medium-potential junction 12 while the remaining electrode 5| is connected to the source of positive potential, +B, through the resistor 52'having such high resistance as not to support steady discharge through the tube. Under such conditions the neon tube electrode 5! will build up potential, if properly insulated, until discharge occurs. but when the quantity of electricity associated with'whatever capacitances are connected to the electrode 51 has been discharged, the tube glow or discharge will stop and-not recommence until these capacitances have been recharged through the resistor 52 to the ignition potential of the tube. A capacitance 56 is provided for the purpose of producing and timing such oscillations, and is connected to electrode II and effectively to ground by connection to the control grid I9 of the beam power tube I I. Since at the time that the relaxation oscillator is called on to operate, the tube II is drawing full current and the path from the control grid is to the grounded cathode 24 is of low impedance, the gas discharged tube condenser 56 at such times is grounded through a low impedance path of' but a few hundred ohms. As a result, when the'gas tube 48 discharge commences, the energy stored in the condenser 56 is rapidly discharged and the potential of the electrode 5| falls abruptly to its extinction potential. The neon tube discharge then is extinguished and the condenser 56 commences recharging at a rate depending on the product of its capacitance and of the resistance 52. This process is repeated, constituting anoscillation of sawtooth form having an abrupt front edge and sloping trailing edge.

This oscillating action will, however, occur only if the electrode 5| of the neon tube 48 is appropriately isolated. This electrode is connected not only to the resistor 52 but also to the anodes 53 and 54 of the triodes 38 and 39. The purpose of these anode connections, in addition tothe provision of positive anode potential for the triodes, is to control the neon oscillator so as to permit it to oscillate while the multivibrator is in its non-oscillating condition, but to prevent the neon oscillator from oscillating while the multivibrator is oscillating. 'Ihese purposes are accomplished in the following manner. When both multivibrator tubes simultaneously conduct, thus preventing them from generating oscillations, the anodes l3 and I! are at some low potential, say +10 volts, holding the triode control grids 4i and 42at the same level of +10 volts.

However, the triode cathodes being at the potential of the junction p, for example, volts, the triodes are thereby held below cutoff, conduct no current, and therefore affect the isolation and insulation of the neon tube electrode 55. The neon tube accordingly is permitted to oscillate. Periodic abrupt negative potential pulses of 20 volts are impressed by the oscillation of the neon tube through-the condenser 56 on the multivibrator grid I 9, decreasing the, current fiow through the beam-power tube M. This pulse is regeneratively repeated through the coupling condensers l4 and i8 between the tubes H and 12 to stop nearly all current fiow through tube ii, after which the multivibrator generates oscillations as previously described. In oscillating, one or the other of the multivibrator tube anodes i3 or I] is at all times almost or quite at the potential of the junction p, causing the associated triode to draw anode current and to have a low impedance, thus maintaining the average potential of the electrode 5i of the neon tube near the potential of its other electrode 49. Since the neon tube requires approximately 75 volts to 'fire, when its potential is thus maintained below 75 volts it cannot fire, is held out of operation and has no effect whatever upon the behavior of the multivibrator generator.

What is claimed is:

l. A square wave generatorcomprising, a freerunning multivibrator, a gas discharge tube relaxation'oscillator, means for coupling the Oscillatory circuit of said gas discharg tube relaxation oscillator to the oscillatory circuit of said free-running multivibrator whereby said freerunning multivibrator is automatically started, and means for preventing the oscillation of said gas discharge tube relaxation oscillator during 2. A square wave generator comprising, a freerunning multivibrator, a gas discharge tube relaxation oscillator, impedance means common to the oscillatory circuits of said gas discharge tube relaxation oscillator and of said free-running multivibrator whereby said free-running multivibrator is automatically started, and means for preventing the oscillation of said gas discharge tube relaxation oscillator during the generation of square waves by said free-running multivibrator.

3. A square wave generator comprising, a freerunning multivibrator comprising two discharge tubes, a gas discharge tub relaxation oscillator comprising a resistance-capacitance timing circuit, an electrical connection means for placing the control electrode to cathode space of one of said free-running multivibrator discharge tubes in series with the resistance-timing circuit of said gas discharge tube relaxation oscillator whereby said free-running multivibrator is automatically started, and means for preventing the oscillation of said gas discharge tube relaxation oscillator during the generation of square waves by said free-running multivibrator.

4. A square wave generator comprising, a freerunning multivibrator, a gas discharge tube relaxation oscillator, an electrical connection from a high potential point in the oscillatory circuit of said gas discharge tube relaxation, oscillator to a point in the oscillatory circuit of said freerunning multivibrator whereby said free-running multivibrator is automatically started, and means for preventing the oscillation of said gas discharge tube relaxation oscillator. during the generation of square waves by said free-running multivibrator.

5. A square wave generator comprising, a pair of discharge tubes having the anode of each interconnected with the control electrode of the other to constitute a free-running multivibrator, a gas discharge tube relaxation oscillator including a resistance-capacitance timing circuit, circuit means connecting said capacitance to the control electrode of one of said pair of discharge tubes whereby signal pulses generated by said relaxation oscillator are impressed on said multivibrator to start operation thereof and means for preventing operation of said relaxation oscillator during the operation or said multivibrator.

6. A square wave generator comprising, a pair of discharge tubes having the anodes of each interconnected with the control electrode of the other to constitute a free-running multivibrator, a gas discharge tube relaxation oscillator having its output connected to one of said pair of discharge tubes whereby signal pulses produced by said relaxation oscillator initiate operation oi said multivibrator, a second pair of discharge tubes having their anode-cathode paths connected in shunt to said gas discharge tube, circuit means connecting respective ones of said second pair of discharge tubes to the respective tubes of said first mentioned pair of discharge tubes for rendering a respective one of said second pair of discharge tubes conductive when the respective tube of said first mentioned pair to which it is connected is rendered non-conductive whereby said gas discharge tub is shunted by a low impedance path and rendered inoperative when said multivibrator is rendered operative.

'7. A square wave generator comprising, a pair of discharge tubes having the anode of each interconnected with the control electrode or the other to constitute a free-running multivibrator, a gas discharge tube relaxation oscillator including a resistance-capacitance timing circuit, circuit means connecting said capacitance to the control electrode of one of said pair of discharge tubes whereby signal pulses generated by said relaxation oscillator are impressed on said multivibrator to initiate operation thereof, a second pair of discharge tubes having their anodecathode paths connected in shunt to said gas discharge tube, circuit means connecting respective ones-of said second pair of discharge tubes to respective tubes of said first mentioned pair of discharge tubes for rendering a respective one of said second pair of discharge tubes conductive when the respective tube of said first mentioned pair'to which it is connected is rendered nonconductive whereby said gas discharge tube is shunted by a low impedance path and rendered inoperative when said multivibrator is rendered I operative.

8. A square wave generator comprising, a pair of discharge tubes having the anode of each interconnected with the control electrode of the other to constitute a free-running multivibrator, a gas discharge tube having at least two electrodes, a source of potential supply, a resistor connected between said source of supply and one electrode of said gas discharge tube, a condenser connected between said one electrode and a control electrode of one of said discharge tubes whereby said gas discharge tube operates asa relaxation oscillator and the signal pulses produced thereby are impressed on one of said discharge tubes to initiate operation of said multivibrator, and means including a second pair of discharge tubes connected to said first mentioned discharge tubes and said gas discharge tube for inhibiting the operation thereof when said multivibrator is rendered operative.

9 A square wave generator comprising, a pair of discharge tubes having the anode of each interconnected with the control electrode of the other to constitute a free-running multivibrator, a gas discharge tube having at least two electrodes, a source of potential supply,'a resistor connected between said source of supply and one electrode of said gas discharge tube, a condenser connected between said one electrode and a control electrode of one of said pair of discharge tubes, whereby said gas discharge tube operates as a relaxation oscillator and the signal pulses produced thereby are impressed on one of said discharge tubes to initiate operation of said multivibrator, a second pair of discharge tubes having their anode-cathode paths connected in shunt to said gas discharge tube, circuit means connecting one of said second pair of discharge tubes to one of said first mentioned pair of discharge tubes, circuit means connecting the other of said second pair of discharge tubes to the other of said first pair of discharge tubes whereby a respective one of said second pair of discharge tubes is rendered conductive when the respective tube of said first mentioned pair to which it is connected is rendered non-conductive and said gas discharge tube shunted by a low impedance path and rendered inoperative when said multivibrator is'rendered operative.

10. A square wave generator comprising, a pair of discharge tubes having the anode of each interconnected with the control electrode of the other to constitute a free-running multivibrator,

a gas discharge tube having two electrodes, a

source of potential supply, a resistor connected between a positive terminal of said potential supply source and one electrode of said gas discharge tube, a condenser connected between said one electrode and a terminal of low potential whereby said gas discharge tube, said resistor and condenser constitute a relaxation oscillator, a circuit connecting said condenser to a control electrode of one of said pair of discharge tubes whereby the signal pulses generated by said relaxation oscillator are impressed on said one discharge tube to initiate operation of said multivibrator, a second pair of discharge tubes having their anodes connected to one of said gas discharge tube electrodes and their cathodes connected to the other gas discharge tube electrode, a circuit connecting the control electrode of one of said second pair of discharge tubes to the anode of one of said first pair of discharge tubes, a circuit connecting the control electrode of the other of said second pair of discharge tubes to the anode of the other of said first mentioned pair of discharge tubes and resistors connected between each of the control electrodes of said second pair of discharge tubes and a positive terminal of said supply source.

11. A square wave generator comprising, a pair of discharge tubes having the anode of each interconnected with the control electrode of the other to constitute a free-running multivibrator, a gas discharge tube having two electrodes, 2. source of potential supply, a resistor connected between a positive terminal of said potential supply source and one electrode of said gas discharge tube, a condenser connected between said one electrode and a terminal of low potential whereby said resistor and condenser constitute a timing circuit and together with said gas discharge tube form a relaxation oscillator circuit, a connection between the control electrode of one of said discharge tubes and said timing circuit whereby the signal pulses produced therein by said relaxation oscillator circuit are impressed on said one discharge tube to initiate operation of said multivibrator, a second pair of discharge tubes having their anodes connected to one of said gas discharge tube electrodes and their cathodes connected to the other of said gas discharge tube electrodes, a circuit connecting the control electrode of one of said second pair of discharge tubes to the anode of one of said first mentioned pair of discharge tubes, a circuit connecting the control electrode of the other of said second pair of discharge tubes to the anode of the other of said first mentioned pair of discharge tubes, resistors connected between each of the control electrodes of said second pair of discharge tubes and a positive terminal of said supply source, the cathodes of said second pair of discharge tubes being connected to a positive terminal of lower potential than the positive terminal of said supply source and a circuit for impressing a direct current on the inputs of said first mentioned discharge tubes.

JOHN W. GRAY.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,452,549 Cleeton Nov. 2, 1948 2,510,167 Boothroyd June 6, 1950 2,557,085 Fisk June 19, 1951 

